System for determining final position of teeth

ABSTRACT

An apparatus and method define a fit a set of upper and lower teeth in a masticatory system of a patient by generating a computer representation of the masticatory system of the patient; and determining an occlusion from the computer representation of the masticatory system using one or more keys.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 10/047,078 (Attorney Docket No. 018563-005110/AT-00108.1),filed Jan. 14, 2002, which was a continuation of application Ser. No.09/313,291 (Attorney Docket: 18563-005100/AT-00108), filed May 13, 1999,now U.S. Pat. No. 6,406,292, which was a non-provisional of ApplicationNo. 60/110,189, filed Nov. 30, 1998. The full disclosures of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is related generally to the field oforthodontics, and more particularly to a system and a method forgradually repositioning teeth.

[0003] A fundamental objective in orthodontics is to realign a patient'steeth to positions where the teeth function optimally and aesthetically.Typically, appliances such as braces are applied to the teeth of thepatient by a treating orthodontist. Each appliance exerts continualforces on the teeth which gradually urge the teeth toward their idealpositions. Over a period of time, the orthodontist adjusts theappliances to move the teeth toward their final destination.

[0004] The process of attaching the braces to teeth is tedious andpainful. Additionally, each visit to the orthodontist is time consumingand expensive. The process is further complicated by uncertainties indetermining a final arrangement for each tooth. Generally, the finaltooth arrangement is determined by the treating orthodontist who writesa prescription. Traditionally, the prescription is based on theorthodontist's knowledge and expertise in selecting the intended finalposition of each tooth and without a precise calculation of forces beingexerted on the teeth when they contact each other.

BRIEF SUMMARY OF THE INVENTION

[0005] The invention provides a method for defining a fit for a set ofupper and lower teeth in a masticatory system of a patient. The fit isdefined by generating a computer representation of the masticatorysystem of the patient and determining an occlusion from the computerrepresentation of the masticatory system using one or more keys.

[0006] Implementations of the invention include one or more of thefollowing. The key can be selected from a group consisting of a molarrelationship, a crown angulation, a crown inclination, teeth rotations,teeth contact points, and an occlusal plane. Where the key is based on amolar relationship, a first permanent molar may be occluded with asecond permanent molar. Where the first permanent molar has a distobuccal cusp with a distal surface and the second permanent molar has amesiobuccal cusp with a mesial surface, the distal surface can occludewith the mesial surface. The mesiobuccal cusp can occlude in a groovebetween mesial and middle cusps of the first permanent molar. The mesialsurface can approach the distal surface. Moreover, the canines andpremolars of the teeth have a cusp-embrasure relationship buccally and acusp-fossa relationship lingually.

[0007] Where the key is based on an angulation of a crown, the methodcan determine a distal inclination of a gingival portion of the crown.The distal inclination can be held constant for all teeth or can beconstant within each tooth type. The angulation can be determinedbetween a facial axis of the clinical crown (FACC) and a lineperpendicular to an occlusal plane. The angulation can be minimized,positive or negative in value.

[0008] Where the key is based on a crown inclination, the method candetermine an angle formed by a line perpendicular to an occlusal planeand a line tangent to a bracket site. The crown inclination can benegative when measured from an upper canine through an upper secondpremolar. The crown inclination can be progressively more negative whenmeasured from a lower canine through a lower second molar. The crowninclination can be between a line parallel and tangent to a facial axisof the clinical crown (FACC) at its midpoint and a line perpendicular toan occlusal plane.

[0009] The key can be based on tooth rotation, or on positions where theteeth are free of undesirable rotations. The key can be based on a toothcontact point, where the contact point can be tight, where no spacesexist between contact points. The key can be based on an occlusal plane.The plane can range between flat to curves of Spee. The curve of Speecan be deep, slight, or reversed.

[0010] The method also includes optimizing a final placement of theteeth. The method can also include identifying one or more featuresassociated with the teeth; and generating a model of the teeth based onthe identified features. The features can be identified automatically orby a user. The computer representation can be an ideal model set ofteeth which can be derived from a cast of the patient's teeth or from apatient with a good occlusion. The method also includes generatingprogress reports associated with the determined occlusion. Generatedreports can be browsed over a network such as a wide area network (theInternet) or a local area network. The progress report can be viewed bya patient or a clinician. The user, which can be a clinician or apatient, manipulates the computer representation of the masticatorysystem.

[0011] The method also includes generating a model the teeth; andadjusting teeth position in the model by following a prescription. Themethod further includes generating a model of the teeth, the modelhaving a visual appearance; and adjusting teeth position in the modeluntil the visual appearance of the model is satisfactory. The model canbe based on an abstract model of idealized teeth placement. The abstractmodel can be specified by one or more arch forms, or can be specifiedusing one or more features associated with the teeth. The teeth positioncan be customized to the patient's teeth.

[0012] In another aspect, a system for generating one or more appliancesfor a patient includes a processor; a display device coupled to theprocessor; a data storage device coupled to the processor; a scannercoupled to the processor for providing data to model the masticatorysystem; means for defining a fit between a set of upper and lower teethin a masticatory system of the patient; and a dental appliancefabrication machine coupled to the processor for generating theappliances in accordance with the fit of the teeth.

[0013] Advantages of the invention include one or more of the following.When a prescription or other final designation is provided, a computermodel can be generated and manipulated to match the prescription. Theprescription may be automatically interpreted in order to generate animage as well as a digital data set representing the final tootharrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is an elevational diagram showing the anatomicalrelationship of the jaws of a patient.

[0015]FIG. 2A illustrates in more detail the patient's lower jaw andprovides a general indication of how teeth may be moved by the methodsand apparatus of the present invention.

[0016]FIG. 2B illustrates a single tooth from FIG. 2A and defines howtooth movement distances are determined.

[0017]FIG. 2C illustrates the jaw of FIG. 2A together with anincremental position adjustment appliance which has been configuredaccording to the methods and apparatus of the present invention.

[0018]FIG. 3 is a block diagram illustrating a process for producingincremental position adjustment appliances.

[0019]FIG. 4 is a flow chart illustrating a process for optimizing afinal placement of the patient's teeth.

[0020]FIG. 5 is a flow chart illustrating a process for performingfunctional occlusion on the patient's teeth.

[0021]FIG. 6 is a flow chart illustrating an optional process forincorporating midtreatment information to the final placement of thepatient's teeth.

[0022]FIG. 7 is flow chart illustrating a process for optimizingocclusion based on one or more keys.

[0023]FIG. 8 is a flow chart illustrating a second process forperforming functional occlusion on the patient's teeth.

[0024]FIG. 9 is a block diagram illustrating a system for generatingappliances in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 shows a skull 10 with an upper jaw bone 22 and a lower jawbone 20. The lower jaw bone 20 hinges at a joint 30 to the skull 10. Thejoint 30 is called a temporomandibular joint (TMJ). The upper jaw bone22 is associated with an upper jaw 101, while the lower jaw bone 20 isassociated with a lower jaw 100.

[0026] A computer model of the jaws 100 and 101 is generated, and acomputer simulation models interactions among the teeth on the jaws 100and 101. The computer simulation allows the system to focus on motionsinvolving contacts between teeth mounted on the jaws. The computersimulation allows the system to render realistic jaw movements which arephysically correct when the jaws 100 and 101 contact each other. Themodel of the jaw places the individual teeth in a treated position.Further, the model can be used to simulate jaw movements includingprotrusive motions, lateral motions, and “tooth guided” motions wherethe path of the lower jaw 100 is guided by teeth contacts rather than byanatomical limits of the jaws 100 and 101. Motions are applied to onejaw, but may also be applied to both jaws. Based on the occlusiondetermination, the final position of the teeth can be ascertained.

[0027] Referring now to FIG. 2A, the lower jaw 100 includes a pluralityof teeth 102, for example. At least some of these teeth may be movedfrom an initial tooth arrangement to a final tooth arrangement. As aframe of reference describing how a tooth may be moved, an arbitrarycenterline (CL) may be drawn through the tooth 102. With reference tothis centerline (CL), each tooth may be moved in orthogonal directionsrepresented by axes 104, 106, and 108 (where 104 is the centerline). Thecenterline may be rotated about the axis 108 (root angulation) and theaxis 104 (torque) as indicated by arrows 110 and 112, respectively.Additionally, the tooth may be rotated about the centerline, asrepresented by an arrow 114. Thus, all possible free-form motions of thetooth can be performed.

[0028]FIG. 2B shows how the magnitude of any tooth movement may bedefined in terms of a maximum linear translation of any point P on atooth 102. Each point P₁ will undergo a cumulative translation as thattooth is moved in any of the orthogonal or rotational directions definedin FIG. 2A. That is, while the point will usually follow a nonlinearpath, there is a linear distance between any point in the tooth whendetermined at any two times during the treatment. Thus, an arbitrarypoint P₁ may in fact undergo a true side-to-side translation asindicated by arrow d₁, while a second arbitration point P₂ may travelalong an arcuate path, resulting in a final translation d₂. Many aspectsof the present invention are defined in terms of the maximum permissiblemovement of a point P₁ induced on any particular tooth. Such maximumtooth movement, in turn, is defined as the maximum linear translation ofthat point P₁ on the tooth which undergoes the maximum movement for thattooth in any treatment step.

[0029]FIG. 2C shows one adjustment appliance 111 which is worn by thepatient in order to achieve an incremental repositioning of individualteeth in the jaw as described generally above. The appliance is apolymeric shell having a teeth receiving cavity. This is described inU.S. application Ser. No. 09/169,036, filed Oct. 8, 1998, which claimspriority from U.S. application Ser. No. 08/947,080, filed Oct. 8, 1997,which in turn claims priority from provisional application number06/050,352, filed Jun. 20, 1997 (collectively the “prior applications”),the full disclosures of which are incorporated by reference.

[0030] As set forth in the prior applications, each polymeric shell maybe configured so that its tooth receiving cavity has a geometrycorresponding to an intermediate or final tooth arrangement intended forthe appliance. The patient's teeth are repositioned from their initialtooth arrangement to a final tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Theadjustment appliances are generated at the beginning of the treatment,and the patient wears each appliance until the pressure of eachappliance on the teeth can no longer be felt. At that point, the patientreplaces the current adjustment appliance with the next adjustmentappliance in the series until no more appliances remain. Conveniently,the appliances are generally not affixed to the teeth and the patientmay place and replace the appliances at any time during the procedure.The final appliance or several appliances in the series may have ageometry or geometries selected to overcorrect the tooth arrangement,i.e., have a geometry which would (if fully achieved) move individualteeth beyond the tooth arrangement which has been selected as the“final.” Such overcorrection may be desirable in order to offsetpotential relapse after the repositioning method has been terminated,i.e., to permit some movement of individual teeth back toward theirprecorrected positions. Overcorrection may also be beneficial to speedthe rate of correction, i.e., by having an appliance with a geometrythat is positioned beyond a desired intermediate or final position, theindividual teeth will be shifted toward the position at a greater rate.In such cases, the use of an appliance can be terminated before theteeth reach the positions defined by the appliance.

[0031] The polymeric shell 111 can fit over all teeth present in theupper or lower jaw. Often, only certain one(s) of the teeth will berepositioned while others of the teeth will provide a base or an anchorregion for holding the appliance 111 in place as the appliance 111applies a resilient repositioning force against the tooth or teeth to berepositioned. In complex cases, however, multiple teeth may berepositioned at some point during the treatment. In such cases, theteeth which are moved can also serve as a base or anchor region forholding the repositioning appliance.

[0032] The polymeric appliance 111 of FIG. 2C may be formed from a thinsheet of a suitable elastomeric polymer, such as Tru-Tain 0.03 in,thermal forming dental material, available from Tru-Tain Plastics,Rochester, Minn. Usually, no wires or other means will be provided forholding the appliance in place over the teeth. In some cases, however,it will be desirable or necessary to provide individual anchors on teethwith corresponding receptacles or apertures in the appliance 100 so thatthe appliance can apply an upward force on the tooth which would not bepossible in the absence of such an anchor.

[0033]FIG. 3 shows a process 200 for producing the incremental positionadjustment appliances for subsequent use by a patient to reposition thepatient's teeth. As a first step, an initial digital data set (IDDS)representing an initial tooth arrangement is obtained (step 202). TheIDDS may be obtained in a variety of ways. For example, the patient'steeth may be scanned or imaged using X-rays, three dimensional X-rays,computer-aided tomographic images or data sets, or magnetic resonanceimages, among others. The teeth data may be generated by a destructivescanner, as described in the incorporated-by-reference U.S. applicationSer. No. 09/169,034, filed Oct. 8, 1998.

[0034] The IDDS is then manipulated using a computer having a suitablegraphical user interface (GUI) and software appropriate for viewing andmodifying the images. More specific aspects of this process will bedescribed in detail below.

[0035] Individual tooth and other components may be segmented orisolated in the model to permit their individual repositioning orremoval from the digital model. After segmenting or isolating thecomponents, the user will often reposition the tooth in the model byfollowing a prescription or other written specification provided by thetreating professional. Alternatively, the user may reposition one ormore teeth based on a visual appearance or based on rules and algorithmsprogrammed into the computer. Once the user is satisfied, the finalteeth arrangement is incorporated into a final digital data set (FDDS)(step 204). The FDDS is used to generate appliances that move the teethin a specified sequence. First, the centers of each tooth model may bealigned using a number of methods. One method is a standard arch. Then,the teeth models are rotated until their roots are in the propervertical position. Next, the teeth models are rotated around theirvertical axis into the proper orientation. The teeth models are thenobserved from the side, and translated vertically into their propervertical position. Finally, the two arches are placed together, and theteeth models moved slightly to ensure that the upper and lower archesproperly mesh together. The meshing of the upper and lower archestogether is visualized using a collision detection process to highlightthe contacting points of the teeth.

[0036] Based on both the IDDS and the FDDS, a plurality of intermediatedigital data sets (INTDDSs) are defined to correspond to incrementallyadjusted appliances (step 206). Finally, a set of incremental positionadjustment appliances are produced based on the INTDDs and the FDDS(step 208).

[0037] In step 204, final positions for the upper and lower teeth in amasticatory system of a patient are determined by generating a computerrepresentation of the masticatory system. An occlusion of the upper andlower teeth is computed from the computer representation; and afunctional occlusion is computed based on interactions in the computerrepresentation of the masticatory system. The occlusion may bedetermined by generating a set of ideal models of the teeth. Each idealmodel in the set of ideal models is an abstract model of idealized teethplacement which is customized to the patient's teeth, as discussedbelow. After applying the ideal model to the computer representation,and the position of the teeth is optimized to fit the ideal model. Theideal model may be specified by one or more arch forms, or may bespecified using various features associated with the teeth.

[0038]FIG. 4 illustrates a process 300 which optimizes the finalplacement of the teeth based on teeth features. First, the process 300automatically or, with human assistance, identifies various featuresassociated with each tooth to arrive at a model of the teeth (step 302).An ideal model set of teeth is then generated either from casts of thepatient's teeth or from patients with a good occlusion (step 303).

[0039] From step 302, the process 300 positions the model of the teethin its approximate final position based on a correspondence of featuresto the ideal model (step 304). In that step, each tooth model is movedso that its features are aligned to the features of a correspondingtooth in the ideal model. The features may be based on cusps, fossae,ridges, distance-based metrics, or shape-based metrics. Shape-basedmetrics may be expressed as a function of the patient's arches, amongothers.

[0040] For example, cusp features associated with each tooth may beused. Cusps are pointed projections on the chewing surface of a tooth.In a detection stage, a possible cusp is viewed as an “island” on thesurface of the tooth, with the candidate cusp at the highest point onthe island. “Highest” is measured with respect to the coordinate systemof the model, but could just as easily be measured with respect to thelocal coordinate system of each tooth. The set of all possible cusps isdetermined by looking for all local maxima on the tooth model that arewithin a specified distance of the top of the bounding box of the model.First, the highest point on the model is designated as the firstcandidate cusp. A plane is passed through this point, perpendicular tothe direction along which the height of a point is measured. The planeis then lowered by a small predetermined distance along the Z axis.Next, all vertices connected to the tooth and which are above the planeand on some connected component are associated with the candidate cuspas cusps. This step is also referred to as a flood fill step. From eachcandidate cusp point, outward flooding is performed, marking each vertexon the model visited in this matter as part of the correspondingcandidate cusp. After the flood fill step is complete, every vertex onthe model is examined. Any vertex that is above the plane and has notbeen visited by one of the flood fills is added to the list of candidatecusps. These steps are repeated until the plane is traveled a specifieddistance.

[0041] After the detection stage, the cusp detection process may includea rejection stage where local geometries around each of the cuspcandidates are analyzed to determine if they possess non-cusp-likefeatures. Cusp candidates that exhibit non-cusp-like features areremoved from the list of cusp candidates. Various criteria may be usedto identify non-cusp-like features. According to one test, the localcurvature of the surface around the cusp candidate is used to determinewhether the candidate possesses non-cusp-like features. Alternatively, ameasure of smoothness is computed based on the average normal in an areaaround the candidate cusp. If the average normal deviates from thenormal at the cusp by more than a specified amount, the candidate cuspis rejected.

[0042] Next, the process 300 computes an orthodontic/occlusion index(step 306). One index which may be used is the PAR (Peer AssessmentRating) index. In addition to PAR, other metrics such as shape-basedmetrics or distance-based metrics may be used.

[0043] The PAR index identifies how far a tooth is from a goodocclusion. A score is assigned to various occlusal traits which make upa malocclusion. The individual scores are summed to obtain an overalltotal, representing the degree a case deviates from normal alignment andocclusion. Normal occlusion and alignment is defined as all anatomicalcontact points being adjacent, with a good intercuspal mesh betweenupper and lower buccal teeth, and with nonexcessive overjet andoverbite.

[0044] In PAR, a score of zero would indicate good alignment, and higherscores would indicate increased levels of irregularity. The overallscore is recorded on pre- and posttreatment dental casts. The differencebetween these scores represents the degree of improvement as a result oforthodontic intervention and active treatment. The eleven components ofthe PAR Index are: upper right segment; upper anterior segment; upperleft segment; lower right segment; lower anterior segment; lower leftsegment; right buccal occlusion; overjet; overbite; centerline; and leftbuccal occlusion. In addition to the PAR index, other indices may bebased on distances of the features on the tooth from their idealpositions or ideal shapes.

[0045] From step 306, the process 300 determines whether additionalindex-reducing movements are possible (step 308). Here, all possiblemovements are attempted, including small movements along each major axisas well as small movements with minor rotations. An index value iscomputed after each small movement and the movement with the best resultis selected. In this context, the best result is the result thatminimizes one or more metrics such as PAR-based metrics, shape-basedmetrics or distance-based metrics. The optimization may use a number oftechniques, including simulated annealing technique, hill climbingtechnique, best-first technique, Powell method, and heuristicstechnique, among others. Simulated annealing techniques may be usedwhere the index is temporarily increased so that another path in thesearch space with a lower minimum may be found. However, by startingwith the teeth in an almost ideal position, any decrease in the indexshould converge to the best result.

[0046] In step 308, if the index can be optimized by moving the tooth,incremental index-reducing movement inputs are added (step 310) and theprocess loops back to step 306 to continue computing theorthodontic/occlusion index. Alternatively, in the event that the indexcannot be optimized any more, the process 300 exits (step 312).

[0047] Turning now to FIG. 5, a process 320 for performing functionalocclusion is shown. Functional occlusion is a process for determininghow well the teeth fit together when the jaws move. The process 320first acquires tooth/arch jaw registration. This may be done usingconventional techniques such as X-ray, a computer tomography, or amechanical device such as a face bow transfer.

[0048] After acquiring the registration information, the process 320places digital dental models of the teeth in a digital articulationsimulator (step 324). The articulation simulator allows a subset of jawmovements such as bite-movements to be simulated, as described below.

[0049] From step 324, the process 320 simulates jaw motions (step 326).A simplified set of movement physics (kinematics) is applied to thedental models. The process 320 performs a simulation using a simplifiedset of interacting forces on the jaws 100 and 101 in relation to oneanother. The simplified physical simulation allows the system to focuson motions involving much contact between the jaws. The physicalsimulation allows the system to render realistic physically correct jawmovements when the jaws 100 and 101 come into contact with each other.

[0050] A range of simulated motion may be supplied using a library ofmotions. One typical motion supplied by the library is a protrusivemotion where the lower jaw 101 is moved forward and backward to bringthe front teeth on both jaws into contact with each other. Anothermotion is a lateral motion found in food chewing. The lateral motioninvolves moving the jaws 100 and 101 side to side. Other motions thatmay be supplied in the library include motions that are “tooth guided”where the path of the lower jaw 100 is guided by the teeth in contactwith each other.

[0051] Next, the process 320 adjusts the final position based oncontacts observed during the simulation of motions in step 326 (step328). The result of the simulation is analyzed, the position of eachtooth can be adjusted if contacts associated with that tooth are deemedexcessive.

[0052] Finally, based on the contact data generated, the processdetermines whether additional motion simulations need to be done. Themotion simulation may be rerun until the contacts associated with eachtooth are acceptable to the treating orthodontist. The tooth modelmanipulation process can be done subjectively, i.e., the user may simplyreposition teeth in an aesthetically and/or therapeutically desiredmanner based on observations of the final position or based on thesimulation of contacts. Alternatively, rules and algorithms may be usedto assist the user in repositioning the teeth based on the contacts. Ifthe simulation needs to be repeated, the process loops back to step 326(step 330). Alternatively, the process exits (step 332).

[0053]FIG. 6 shows an optional process of 340 of incorporatingmidtreatment information to the final positioning process. First, adigital model incorporating dental information associated with thepatient is generated from a scan of the patient's teeth (step 342). Thescan may be performed using casts, X-rays or any of the conventionalscanning methods.

[0054] Next, the digital model is segmented into one model for eachtooth (step 344). Each tooth is then matched against a model associatedwith a prior scan developed at the beginning of the treatment plan (step346). The matching process is based on matching corresponding pointsbetween the current scan and the prior scan of the teeth. In most cases,the teeth segmented from the current scan retain the shapes determinedat the beginning of the treatment plan, and the matching process is easybecause the models should be similar to each other.

[0055] A final position transform is then applied to the new teeth model(step 348). The final position and specification from the prior model iscopied to the current model of the patient, and the final position isadjusted based on the new models, the new X-ray information or a newprescription (step 350). Step 350 basically involves rerunning theminimization process 300 (FIG. 4) described previously with the newinformation, which may be a slight change in the model, a change in theX-ray scan, or a change the prescription. Finally, the process 340 exits(step 352)

[0056]FIG. 7 is a flowchart of a process 400 for determining optimalocclusion in the teeth model. The process 400 optimizes the occlusionbased on six characteristics (Six Keys) that were found to beconsistently present in a collection of 120 casts of naturally optimalocclusion. The keys include a molar relationship key, a crown angulationkey, a crown inclination key, teeth rotation key, teeth contact pointkey, and an occlusal plane key. The individual keys provide a completeset of indicators of optimal occlusion, can be judged from tangiblelandmarks, and can be judged from a facial and occlusal surfaces of thecrowns, thus reducing the need for a lingual view for articulating paperto confirm occlusial interfacing. These keys are described in LawrenceF. Andrews, “The six keys to normal occlusion,” Am. J. Orthod. Vol. 62,No. 3 pp.296-309 (9/72) and in Chapter 3 of his book entitled StraightWire—The Concept and Appliance (Published by L. A. Wells), the contentsof which are incorporated by reference.

[0057] The Six Keys are interdependent elements of the structural systemof optimal occlusion and are based on similarities in the patterns ofangulation, inclination, shape, and relative size (facial prominence) oftooth types. As such, they serve as a base for evaluating occlusion. TheSix Keys are used as treatment objectives for patients. Thecharacteristics of the Six Keys are incorporated into the design ofappliance 111 to enhance precision and consistency in treatment results.

[0058] The process 400 first checks whether optimization is to be donewith respect to a molar relationship key (step 402). If so, the process400 checks and applies an appropriate molar relationship (step 404). Themolar relationship pertains to the occlusion and the interarchrelationships of the teeth. Step 404 enforces the following sevenrequirements of the molar relationship key:

[0059] 1. The mesiobuccal cusp of the permanent maxillary first molaroccludes in the groove between the mesial and the middle buccal cusps ofthe permanent mandibular first molar.

[0060] 2. The distal marginal ridge of the maxillary first molaroccludes with the mesial marginal ridge of the mandibular second molar.

[0061] 3. The mesiolingual cusp of the maxillary first molar occludes inthe central fossa of the mandibular first molar.

[0062] 4. The buccal cusps of the maxillary premolars have acusp-embrasure relationship with the mandibular premolars.

[0063] 5. The lingual cusps of the maxillary premolars have a cusp-fossarelationship with the mandibular premolars.

[0064] 6. The maxillary canine has a cusp-embrasure relationship withthe mandibular canine and first premolar. The tip of its cusp isslightly mesial to the embrasure.

[0065] 7. The maxillary incisors overlap the mandibular incisors and themidlines of the arches match.

[0066] The cusp-groove and the marginal-ridge conditions of the molars,the cuspembrasure relationship of the premolars and canines, and incisoroverjet can be observed directly from the buccal perspective. A facialaxis of the clinical crown (FACC) measurement is used to permitassessment of the lingual-cusp occlusion of the molars and premolarswhen these teeth are viewed from their mesiobuccal aspect, as explainedbelow.

[0067] In step 404, Interarch relationship of the posterior teeth of twodentitions can be the same, but the interfacing of the occlusal surfacesof the two dentitions may differ because of differing crowninclinations.

[0068] Step 404 ensures that correct occlusal interfacing throughcorrect interarch relationship, angulation, and crow inclination.Interarch relationship and angulation are best judged from the buccalperspective; crown inclination for posterior teeth is best judged fromthe dentition's mesiobuccal perspective. Judging posterior occlusionfirst from the buccal (for angulation and interarch relationship) thenfrom the mesiobuccal (for inclination) provides a perspective that canbe systematically described and quantified. Such information, along withother nonocclusal guidelines, are used in step 404 to identify occlusaldeviations.

[0069] Step 404 includes occluding a first permanent molar with a secondpermanent molar. In such an occlusion, the first permanent molar has adistobuccal cusp with a distal surface, the second permanent molar has amesiobuccal cusp with a mesial surface and the distal surface occludeswith the mesial surface. The mesiobuccal cusp can occlude in a groovebetween mesial and middle cusps of the first permanent molar. The mesialsurface can closely approach the distal surface. Moreover, where theteeth have canines and premolars, the canines and premolars have acusp-embrasure relationship buccally and a cusp-fossa relationshiplingually.

[0070] From step 402 to 404, the process 400 checks whether theocclusion needs to be optimized with respect to a crown angulation key(step 406). If so, the occlusion is optimized with respect to the crownangulation key (step 408). Essentially, step 408 ensures that all crownsshould have a positive angulation, and all crowns of each tooth typeshould be similar in the amount of angulation. Further, the contact-areaposition for each tooth type should be similar. Step 408 determines adistal inclination of a gingival portion of the crown. The distalinclination may be constant within each tooth type. The angulation maybe determined between the FACC and a line perpendicular to an occlusalplane. Step 408 may minimize the angulation, which may be positive ornegative.

[0071] From step 406 or step 408, the process 400 checks whether theocclusion is to be optimized with respect to a crown inclination key(step 410). If so, the crown inclination optimization is performed (step412). As they do in angulation, consistent patterns also prevail incrown inclination, the following three characteristics for individualteeth are analyzed in step 412.

[0072] 1. Most maxillary incisors have a positive inclination;mandibular incisors have a slightly negative inclination. In most of theoptimal sample, the interincisal crown angle is less than 180°. Thecrowns of maxillary incisors are more positively inclined, relative to aline 90° to the occlusal plane, than the mandibular incisors arenegatively inclined to the same line.

[0073] 2. The inclinations of the maxillary incisor crowns are generallypositive—the centrals more positive than the laterals. Canines andpremolars are negative and quite similar. The inclinations of themaxillary first and second molars are also similar and negative, butslightly more negative than those of the canines and premolars. Themolars are more negative because they are measured from the grooveinstead of from the prominent facial ridge, from which the canines andpremolars are measured.

[0074] 3. The inclinations of the mandibular crowns are progressivelymore negative from the incisors through the second molars.

[0075] In step 412, the crown inclination can represent an angle formedby a line perpendicular to an occlusal plane and a line tangent to abracket site. In this step, the crown inclination can be negative whenmeasured from an upper canine through an upper second premolar. Thecrown inclination may become progressively more negative when measuredfrom a lower canine through a lower second molar. The crown inclinationmay also be positioned between a line parallel and tangent to the FACCat its midpoint and a line perpendicular to an occlusal plane.

[0076] From step 410 or 412, the process 400 checks whether theocclusion is to optimized using a rotation key (step 414). If so, theprocess 400 checks for undesirable rotations (step 416) and corrects themodel so that tooth rotations are absent.

[0077] From step 414 or step 416, the process 400 then determineswhether the occlusion needs to be optimized with respect to spacing(step 418). If so, the process 400 checks for tight contacts that is, nospaces should exist between teeth (step 420). Step 418 checks thatcontact points abut unless a discrepancy exists in mesiodistal crowndiameter.

[0078] From step 418 or step 420, the process 400 then checks whetherthe occlusion is to be optimized with respect to an occlusal plane key(step 422). If so, the process 400 then optimizes the teeth model byanalyzing the plane of occlusion (step 424). In step 424, the depth ofthe curve of Spee ranges from a flat plane to a slightly concavesurface. The plane can range between flat to curves of Spee. Moreover,the curve of Spee may be deep, slight, or reversed. From step 422 orstep 424, the process 400 exits.

[0079]FIG. 8 is a flow chart illustrating a second process fordetremining final position of the patient's teeth. The process of FIG. 8identifies an ideal base model for the final position of the teeth thatconsists of an arch curve (step 450). This model can be selected from asuite of template models, derived from patients with ideal occlusion, orderived from patient under treatment (via the casts, X-rays, aprescription, or data about the patient from other sources). Next, theuser of the software places and orients a marker on each tooth, throughwhich the arch curve (or curves) is intended to pass (step 452). Thecurves can be designed so that they should pass through markers placedon the tooth's facial, lingual, or occlusal surface. Multiple archcurves can be used to make the specification of the final position moreaccurate. In step 454, the position and orientation of the teeth areadjusted so that the arch curve passes through the marker on each toothand the teeth do not overlap. Optionally, the teeth can be made tocontact each other in this step. Next, where the teeth have multiplemarkers, the position and orientation of the tooth is set so that thearch curves pass as closely as possible through all markers on eachtooth (step 456). In another implementation, the markers can beautomatically placed and oriented on each tooth. The user can optionallyadjust their position and orientation.

[0080]FIG. 9 is a simplified block diagram of a data processing system500. Data processing system 500 typically includes at least oneprocessor 502 which communicates with a number of peripheral devicesover bus subsystem 504. These peripheral devices typically include astorage subsystem 506 (memory subsystem 508 and file storage subsystem514), a set of user interface input and output devices 518, and aninterface to outside networks 516, including the public switchedtelephone network. This interface is shown schematically as “Modems andNetwork Interface” block 516, and is coupled to corresponding interfacedevices in other data processing systems over communication networkinterface 524. Data processing system 500 may include a terminal or alow-end personal computer or a high-end personal computer, workstationor mainframe.

[0081] The user interface input devices typically include a keyboard andmay further include a pointing device and a scanner. The pointing devicemay be an indirect pointing device such as a mouse, trackball, touchpad,or graphics tablet, or a direct pointing device such as a touchscreenincorporated into the display. Other types of user interface inputdevices, such as voice recognition systems, may be used.

[0082] User interface output devices may include a printer and a displaysubsystem, which includes a display controller and a display devicecoupled to the controller. The display device may be a cathode ray tube(CRT), a flat-panel device such as a liquid crystal display (LCD), or aprojection device. The display subsystem may also provide non-visualdisplay such as audio output.

[0083] Storage subsystem 506 maintains the basic programming and dataconstructs that provide the functionality of the present invention. Thesoftware modules discussed above are typically stored in storagesubsystem 506. Storage subsystem 506 typically comprises memorysubsystem 508 and file storage subsystem 514.

[0084] Memory subsystem 508 typically includes a number of memoriesincluding a main random access memory (RAM) 510 for storage ofinstructions and data during program execution and a read only memory(ROM) 512 in which fixed instructions are stored. In the case ofMacintosh-compatible personal computers the ROM would include portionsof the operating system; in the case of IBM-compatible personalcomputers, this would include the BIOS (basic input/output system).

[0085] File storage subsystem 514 provides persistent (nonvolatile)storage for program and data files, and typically includes at least onehard disk drive and at least one floppy disk drive (with associatedremovable media). There may also be other devices such as a CD-ROM driveand optical drives (all with their associated removable media).Additionally, the system may include drives of the type with removablemedia cartridges. The removable media cartridges may, for example behard disk cartridges, such as those marketed by Syquest and others, andflexible disk cartridges, such as those marketed by Iomega. One or moreof the drives may be located at a remote location, such as in a serveron a local area network or at a site on the Internet's World Wide Web.

[0086] In this context, the term “bus subsystem” is used generically soas to include any mechanism for letting the various components andsubsystems communicate with each other as intended. With the exceptionof the input devices and the display, the other components need not beat the same physical location. Thus, for example, portions of the filestorage system could be connected over various local-area or wide-areanetwork media, including telephone lines. Similarly, the input devicesand display need not be at the same location as the processor, althoughit is anticipated that the present invention will most often beimplemented in the context of PCS and workstations.

[0087] Bus subsystem 504 is shown schematically as a single bus, but atypical system has a number of buses such as a local bus and one or moreexpansion buses (e.g., ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), aswell as serial and parallel ports. Network connections are usuallyestablished through a device such as a network adapter on one of theseexpansion buses or a modem on a serial port. The client computer may bea desktop system or a portable system.

[0088] Scanner 520 is responsible for scanning casts of the patient'steeth obtained either from the patient or from an orthodontist andproviding the scanned digital data set information to data processingsystem 500 for further processing. In a distributed environment, scanner520 may be located at a remote location and communicate scanned digitaldata set information to data processing system 500 over networkinterface 524.

[0089] Fabrication machine 522 fabricates dental appliances based onintermediate and final data set information received from dataprocessing system 500. In a distributed environment, fabrication machine522 may be located at a remote location and receive data set informationfrom data processing system 500 over network interface 524.

[0090] Various alternatives, modifications, and equivalents may be usedin lieu of the above components. Although the final position of theteeth may be determined using computer-aided techniques, a user may movethe teeth into their final positions by independently manipulating oneor more teeth while satisfying the constraints of the prescription.

[0091] Additionally, the techniques described here may be implemented inhardware or software, or a combination of the two. The techniques may beimplemented in computer programs executing on programmable computersthat each includes a processor, a storage medium readable by theprocessor (including volatile and nonvolatile memory and/or storageelements), and suitable input and output devices. Program code isapplied to data entered using an input device to perform the functionsdescribed and to generate output information. The output information isapplied to one or more output devices.

[0092] Each program can be implemented in a high level procedural orobject-oriented programming language to operate in conjunction with acomputer system. However, the programs can be implemented in assembly ormachine language, if desired. In any case, the language may be acompiled or interpreted language.

[0093] Each such computer program can be stored on a storage medium ordevice (e.g., CD-ROM, hard disk or magnetic diskette) that is readableby a general or special purpose programmable computer for configuringand operating the computer when the storage medium or device is read bythe computer to perform the procedures described. The system also may beimplemented as a computer-readable storage medium, configured with acomputer program, where the storage medium so configured causes acomputer to operate in a specific and predefined manner.

[0094] Further, while the invention has been shown and described withreference to an embodiment thereof, those skilled in the art willunderstand that the above and other changes in form and detail may bemade without departing from the spirit and scope of the followingclaims.

What is claimed is:
 1. A method for defining a fit between a set of upper and lower teeth in a masticatory system of a patient, comprising: generating a computer representation of the masticatory system of the patient; determining an occlusion from the computer representation of the masticatory system using one or more keys; and generating a plurality of appliances based on the occlusion to resiliently reposition the teeth from one arrangement to a successive arrangement.
 2. The method of claim 1, wherein one of the keys is based on a molar relationship.
 3. The method of claim 2, further comprising occluding a first permanent molar with a second permanent molar.
 4. The method of claim 3, wherein the first permanent molar has a disto buccal cusp with a distal surface and the second permanent molar has a mesiobuccal cusp with a mesial surface and wherein the distal surface occludes with the mesial surface.
 5. The method of claim 4, wherein the mesiobuccal cusp occludes in a groove between mesial and middle cusps of the first permanent molar.
 6. The method of claim 3, wherein the mesial surface closely approaches the distal surface.
 7. The method of claim 2, wherein the teeth include canines and premolars and wherein the canines and premolars have a cusp-embrasure relationship buccally and a cusp-fossa relationship lingually.
 8. The method of claim 1, wherein one of the keys is based on an angulation of a crown.
 9. The method of claim 8, wherein the crown has a distal crown tip, further comprising determining a distal inclination of a gingival portion of the crown.
 10. The method of claim 9, wherein the distal inclination is constant.
 11. The method of claim 9, wherein the distal inclination is constant within each tooth type.
 12. The method of claim 9, wherein the angulation is determined between a facial axis of the clinical crown (FACC) and a line perpendicular to an occlusal plane.
 13. The method of claim 12, wherein the angulation is minimized.
 14. The method of claim 8, wherein the angulation is positive.
 15. The method of claim 8, wherein the angulation is negative.
 16. The method of claim 1, wherein one of the keys is based on a crown inclination.
 17. The method of claim 16, wherein the crown inclination represents an angle formed by a line perpendicular to an occlusal plane and the FACC.
 18. The method of claim 16, wherein the crown inclination is negative when measured from an upper canine through an upper second premolar.
 19. The method of claim 16, wherein the crown inclination is progressively more negative when measured from a lower canine through a lower second molar.
 20. The method of claim 16, wherein the crown inclination between a line parallel and tangent to a facial axis of the clinical crown (FACC) at its midpoint and a line perpendicular to an occlusal plane.
 21. The method of claim 1, wherein one of the keys is based on tooth rotation.
 22. The method of claim 21, wherein the teeth & free of undesirable rotations.
 23. The method of claim 1, wherein one of the keys is based on a tooth contact point.
 24. The method of claim 23, wherein the contact point is tight.
 25. The method of claim 23, wherein no spaces exist between contact points.
 26. The method of claim 1, wherein one of the keys is based on an occlusal plane.
 27. The method of claim 26, wherein the plane ranges between flat to curves of Spee.
 28. The method of claim 27, wherein the plane is flat.
 29. The method of claim 27, wherein the plane follows a curve of Spee.
 30. The method of claim 29, wherein the curve of Spee is deep.
 31. The method of claim 29, wherein the curve of Spee is slight.
 32. The method of claim 29, wherein the curve of Spec is reversed.
 33. The method of claim 1, wherein one of the keys is selected from a group consisting of a molar relationship, a crown angulation, a crown inclination, teeth rotations, teeth contact points, and an occlusal plane.
 34. The method of claim 1, further comprising optimizing a final placement of the teeth.
 35. The method of claim 34, further comprising: identifying one or more features associated with the teeth; and generating a model of the teeth based on the identified features.
 36. The method of claim 35, wherein at least one of the feature is identified automatically.
 37. The method of claim 36, wherein at least one of the feature is identified by a user.
 38. The method of claim 35, wherein the ideal model set of teeth is derived from a cast of the patient's teeth.
 39. The method of claim 35, wherein the ideal model set of teeth is derived from a patient with a good occlusion.
 40. The method of claim 1, wherein the computer representation is an ideal model set of teeth.
 41. The method of claim 1, further comprising generating progress reports associated with the determined occlusion.
 42. The method of claim 41, further comprising browsing the generated reports over a network.
 43. The method of claim 42, wherein the network is a wide area network.
 44. The method of claim 43, wherein the wide area network is the Internet.
 45. The method of claim 42, wherein the network is a local area network.
 46. The method of claim 41, wherein the progress report is viewed by a patient.
 47. The method of claim 41, wherein the progress report is viewed by a clinician.
 48. The method of claim 1, wherein the user manipulates the computer representation of the masticatory system.
 49. The method of claim 48, wherein the user is a patient.
 50. The method of claim 49, wherein the user is a clinician.
 51. The method of claim 1, further comprising: generating a model of the teeth; and adjusting teeth position in the model by following a prescription.
 52. The method of claims 51, wherein the model is based on an abstract model of idealized teeth placement.
 53. The method of claim 52, wherein the abstract model is specified by one or more arch forms.
 54. The method of claim 52, wherein the ideal model may be specified using one or more features associated with the teeth.
 55. The method of claim 51, wherein the teeth position is customized to the patient's teeth.
 56. The method of claim 1, further comprising: generating a model of the teeth, the model having a visual appearance; and adjusting teeth position in the model until the visual appearance of the model is satisfactory.
 57. The method of claims 56, wherein the model is based on an abstract model of idealized teeth placement.
 58. A computer-implemented apparatus for defining a fit between a set of upper and lower teeth in a masticatory system of a patient, the apparatus comprising instructions operable to cause a programmable processor to: generate a computer representation of the masticatory system of the patient; determine an occlusion from the computer representation of the masticatory system using one or more keys; and generate a plurality of appliances based on the occlusion to resiliently reposition the teeth from one arrangement to a successive arrangement.
 59. The apparatus of claim 58, wherein one of the keys is based on a molar relationship.
 60. The apparatus of claim 59, further comprising instructions to model the occlusion of a first permanent molar with a second permanent molar.
 61. The apparatus of claim 60, wherein the first permanent molar has a disto buccal cusp with a distal surface and the second permanent molar has a mesiobuccal cusp with a mesial surface and wherein the distal surface occludes with the mesial surface.
 62. The apparatus of claim 61, wherein the mesiobuccal cusp occludes in a groove between mesial and middle cusps of the first permanent molar.
 63. The apparatus of claim 60, wherein the mesial surface closely approaches the distal surface.
 64. The apparatus of claim 59, wherein the teeth include canines and premolars and wherein the canines and premolars have a cusp-embrasure relationship buccally and a cusp-fossa relationship lingually.
 65. The apparatus of claim 58, wherein one of the keys is based on an angulation of a crown.
 66. The apparatus of claim 65, wherein the crown has a distal crown tip, further comprising instructions to determine a distal inclination of a gingival portion of the crown.
 67. The apparatus of claim 66, wherein the distal inclination is constant.
 68. The apparatus of claim 66, wherein the distal inclination is constant within each tooth type.
 69. The apparatus of claim 66, wherein the angulation is determined between a facial axis of the clinical crown (FACC) and a line perpendicular to an occlusal plane.
 70. The apparatus of claim 69, wherein the angulation is minimized.
 71. The apparatus of claim 66, wherein the angulation is positive.
 72. The apparatus of claim 66, wherein the angulation is negative.
 73. The apparatus of claim 72, wherein the crown inclination represents an angle formed by a line perpendicular to an occlusal plane and a line tangent to a bracket site.
 74. The apparatus of claim 58, wherein one of the keys is based on a crown inclination.
 75. The apparatus of claim 74, wherein the crown inclination is negative when measured from an upper canine through an upper second premolar.
 76. The apparatus of claim 74, wherein the crown inclination is progressively more negative when measured from a lower canine through a lower second molar.
 77. The apparatus of claim 74, wherein the crown inclination between a line parallel and tangent to a facial axis of the clinical crown (FACC) at its midpoint and a line perpendicular to an occlusal plane.
 78. The apparatus of claim 58, wherein one of the keys is based on tooth rotation.
 79. The apparatus of claim 78, wherein the teeth are free of undesirable rotations.
 80. The apparatus of claim 58, wherein one of the keys is based on a tooth contact point.
 81. The apparatus of claim 80, wherein the contact point is tight.
 82. The apparatus of claim 80, wherein no spaces exist between contact points.
 83. The apparatus of claim 58, wherein one of the keys is based on an occlusal plane.
 84. The apparatus of claim 83, wherein the plane ranges between flat to curves of Spee.
 85. The apparatus of claim 84, wherein the plane is flat.
 86. The apparatus of claim 84, wherein the plane follows a curve of Spec.
 87. The apparatus of claim 84, wherein the curve of Spee is deep.
 88. The apparatus of claim 86, wherein the curve of Spee is slight.
 89. The apparatus of claim 86, wherein the curve of Spec is reversed.
 90. The apparatus of claim 58, wherein one of the keys is selected from a group consisting of a molar relationship, a crown angulation, a crown inclination, teeth rotations, teeth contact points, and an occlusal plane.
 91. A system for defining a fit between a set of upper and lower teeth in a masticatory system of a patient, comprising: a processor; a display device coupled to the processor; and a data storage device coupled to the processor, the data storage device storing instructions operable to cause the processor to: generate a computer representation of the masticatory system of the patient; and determine an occlusion from the computer representation of the masticatory system using one or more keys; and generate a plurality of appliances based on the occlusion to resiliently reposition the teeth from one arrangement to a successive arrangement.
 92. The system of claim 91, wherein one of the keys is selected from a group consisting of a molar relationship, a crown angulation, a crown inclination, teeth rotations, teeth contact points, and an occlusal plane.
 93. The system of claim 91, wherein one of the keys is based on molar relationship.
 94. The system of claim 91, wherein one of the keys is based on crown angulation.
 95. The system of claim 91, wherein one of the keys is based on crown inclination.
 96. The system of claim 91, wherein one of the keys is based on tooth rotation.
 97. The system of claim 91, wherein one of the keys is based on a tooth contact point.
 98. The system of claim 91, wherein one of the keys is based on a n occlusal plane.
 99. The system of claim 91, further comprising generating progress reports associated with the occlusion.
 100. The system of claim 99, further comprising browsing the generated reports over the Internet.
 101. The system of claim 91, wherein the data storage device storing instructions operable to cause the processor to identify an ideal base model for the final position of the teeth.
 102. The system of claim 101, wherein the ideal base model includes an arch curve.
 103. The system of claim 101, further comprising instructions to place a marker on each tooth.
 104. The system of claim 103, wherein the marker is oriented through which an arch curve is to pass through the marker.
 105. The system of claim 104, further comprising instructions to adjust the position and orientation of the teeth.
 106. The system of claim 105, further comprising instructions to set the position and orientation of the teeth so that the arch curve passes though the marker within a predetermined deviation.
 107. The system of claim 103, where the instructions allow a user of the system to place the marker.
 108. The system of claim 103, where the instructions automatically place the marker. 